Deploy binddns-auth BIND cluster

Adds the authoritative masters (pod-0 primary + 2 secondaries via catalog/AXFR); includes the catalog zone and transfer TSIG key. Stacked on the bind-operator deploy so the
CRDs and kubeconform schemas are present; merge the operator PR first.

- add apps/base/binddns-auth and its au-syd1 overlay

apps/base/binddns-auth/namespace.yaml

@@ -0,0 +1,5 @@
+---
+apiVersion: v1
+kind: Namespace
+metadata:
+  name: binddns-auth